Rheumatoid arthritis affects millions of Americans. Like osteoarthritis, rheumatoid arthritis occurs more frequently in women than in men. Adult rheumatoid arthritis can occur in people in their 20s and 30s, though it appears more commonly in those over 45 years of age. Researchers now believe that treating rheumatoid arthritis early and aggressively not only may control joint pain, inflammation, and stiffness, but also may slow the progression of the disease.